The present invention relates to an improvement in a throttle body for adjusting a quantity of suction air to be supplied to an internal combustion engine. The throttle body of the present invention includes a suction passage and a throttle valve adapted to be rotated in the suction passage to open and close the same. When a rotational angle or opening of the throttle valve is adjusted, an effective sectional area in the suction passage at the throttle valve is varied to adjust a quantity of suction air.
Normally, the opening of the throttle valve is adjusted by adjusting an operational amount of an accelerator pedal, accelerator lever, etc. (which will be hereinafter also referred to as an accelerator). The present invention relates particularly to a throttle body having an interconnecting lever for converting the operational amount of the accelerator to the opening of the throttle valve, and more particularly to a throttle body utilizing a cam and a cam follower for converting the rotation of the interconnecting lever to the rotation of a throttle valve shaft.
This type of throttle body is disclosed in Japanese Patent Publication Nos. 61-53536, 61-53537 and 61-53538, for example.
In the conventional throttle body, as the operational amount of the accelerator is converted into the opening of the throttle valve by the operation of the interconnecting lever, the relation between the operational amount of the accelerator and the opening of the throttle valve may be considerably freely set by suitably designing a shape of the cam. For example, FIG. 5 shows the relation between a percentage of an actual stroke of the accelerator to an overall stroke thereof or an opening rate of the interconnecting shaft (a rotating shaft for the interconnecting lever) and an opening rate of the throttle valve shaft. Referring to FIG. 5, a straight line X shows the relation in the case that the accelerator is directly connected to the throttle valve without using the interconnecting lever, while a curved line Y shows the relation in the case that the interconnecting lever is used. As apparent from FIG. 5, when the interconnecting lever is not used, the opening of the throttle valve is proportional to the operational amount of the accelerator. To the contrary, when the interconnecting lever is used, a change in the opening of the throttle valve in a certain range of the small opening is relatively dull, while the change in a certain range of the large opening is relatively sharp. According to the relation of the curved line Y, fine adjustment of the opening of the throttle valve may be easily carried out when the opening is in the relatively small range, and the opening in the relatively large range may be made sharply responsive to the operation of the accelerator.
Thus, the throttle body using the interconnecting lever has the above-mentioned advantages, however, it yet has the following problems.
Although the relation between the operational amount of the accelerator and the opening of the throttle valve in the conventional throttle body using the interconnecting lever is satisfactory, there is a problem in an operational force required for operating the accelerator. For example, FIG. 4 shows the relation between the opening of the interconnecting lever and the operational force of the interconnecting shaft. Referring to FIG. 4, a dotted line E, F shows the relation in the prior art (the line E corresponds to a stroke of opening the throttle valve, and the line F corresponds to a stroke of closing the throttle valve), while a solid line G, H shows the relation according to the present invention. As apparent from FIG. 4, the prior art device has a problem such that the operational force is rapidly changed during the stroke, imparting a kind of unnatural feeling to an operator.
Further, the prior art device has another problem such that there is generated an undue frictional force at a contact point between the cam and the cam follower, causing hindrance of smooth accelerator operation.
Additionally, in the prior art device, it is difficult to desirably adjust a relative position of the cam and the cam follower, resulting in dispersion of characteristics of each throttle body as manufactured.